CS Lewis called this sort persuasive argumentation....."coming in the back door." When I go into pagan/agnostic/secular humanist groups, which are most generally designated as dgs for "free-thinkers" my arguments are always couched in secular terms.
Good idea. People often forget that this technique was used by Paul with the Athenians, when he reasoned with them on their level and convinced them that the "Unknown God" they'd been honoring was really Yahweh.